Electromagnetic contactor

ABSTRACT

An electromagnetic contactor having an electromagnet consisting of a fixed core and an operating coil mounted on the fixed core, a plurality of fixed contacts, a crossbar disposed above the fixed core, a plurality of contact bars associated with the crossbar and each provided with a pair of movable contacts located opposite the corresponding fixed contacts, respectively, a movable core joined to the lower portion of the crossbar opposite to the fixed core, and a rigid frame consisting of two parallel polygonal bars and two parallel connecting bars interconnecting the respective opposite ends of the polygonal bars. The crossbar and the movable core are supported pivotally on the rigid frame. One of the polygonal bars is supported rotatably at the opposite ends thereof in bearings provided on a stand, while the other polygonal bar is urged upward by springs so that the rigid frame will swing to bring the movable contacts into contact with the fixed contacts, respectively, when the operating coil is energized to attract the movable core to the fixed core.

BACKGROUND OF THE INVENTION

The present invention relates to an electromagnetic contactor forestablishing and interrupting the main power supply circuit of factoriesor a power supply circuit for a large-scale motor.

A conventional two-contact three-phase electromagnetic contactor employsan integrally formed three-phase crossbar which is movably provided forholding a movable core, wherein the motion of the crossbar is limited bythe gap defined by the base plate fixedly mounted to hold the crossbar.

Therefore, simultaneous contact of the contacts of the three-phasecontactors have been affected by the tilting of the crossbar within saidgap. It is possible to perform a sliding adjustment of the crossbar insmall-sized electromagnetic contactor within a range of allowance topractically negligible extent. In a large sized one, however, thecrossbar having contacts for three phases are invariably formedintegrally. As a result, the preciseness of the thus formed crossbar isaffected to such an extent that the gap must be enlarged at the risk ofexpected simultaneous contact of the contacts for three phases due tothe enlarged tilting of the crossbar.

The present invention is intended to solve the above problem and itsobject is to provide a large-sized electromagnetic contactor in whichsimultaneous contact of the three phase movable and fixed contacts isassured even if the three-phase crossbar is integrally formed.

SUMMARY OF THE INVENTION

Accordingly, the present invention has been made to solve those problemsof the conventional two-contact type three-phase electromagneticcontactor.

It is an object of the present invention to provide a large capacitytwo-contact type three-phase electromagnetic contactor capable ofbringing all the movable contacts thereof simultaneously into contactwith the corresponding fixed contacts.

It is another object of the present invention to provide a largecapacity two-contact type three-phase electromagnetic contactor having aframe of rigid construction for supporting one or a plurality ofcrossbars and a movable core, capable of ensuring the simultaneouscontact of the movable contacts with the corresponding fixed contacts.

According to one aspect of the present invention, there is provided anelectromagnetic contactor comprising: a base plate; a stand fixed to thebase plate; an electromagnet consisting of a fixed core and an operatingcoil and disposed within the stand; a plurality of fixed contactsprovided in the upper portion of the stand; a crossbar disposed abovethe fixed core; a plurality of contact bars each associated with thecrossbar and provided with a pair of movable contacts so that themovable contacts are located opposite the corresponding fixed contacts,respectively; a movable core joined to the lower portion of the crossbarso as to be located opposite the fixed core; and a rigid frameconsisting of two parallel polygonal bars and two parallel connectingbars interconnecting the respective opposite ends of the polygonal bars,and pivotally supporting the assembly of the crossbar and the movablecore at the opposite ends of the movable core, wherein one of thepolygonal bars is supported rotatably at the opposite ends thereof inbearings provided on one side of the stand, while the other polygonalbar is urged upward by springs so that the rigid frame is swingable onthe former polygonal bar, slots and holes are formed in the respectiveopposite ends of the connecting bars, respectively, and the frame isassembled by fitting the respective opposite ends of the polygonal barsinto the corresponding holes of the connecting bars and pressing theslotted outer ends of the connecting bars with screws so as to fastenthe polygonal bars to the connecting bars.

According to another aspect of the present invention, there is providedan electromagnetic contactor comprising: a base plate; a stand fixed tothe base plate; an electromagnetic consisting of a fixed core and anoperating coil and disposed within the stand; a plurality of fixedcontacts provided in the upper portion of the stand; a supporting case;a plurality of crossbars mounted on the supporting case and joined tothe same with pins, respectively; a plurality of contact bars associatedwith the crossbars, respectively, and each provided with a pair ofmovable contacts so that the movable contacts are located opposite thecorresponding fixed contacts, respectively; a movable core disposedwithin the supporting case and joined to the same with the pins joiningthe crossbars to the supporting case, so as to be located opposite thefixed core; and a rigid frame consisting of two parallel polygonal barsand two parallel connecting bars interconnecting the respective oppositeends of the polygonal bars, and pivotally supporting case at theopposite ends of the same, wherein one of the polygonal bars issupported rotatably at the opposite ends thereof in bearings provided onone side of the stand, while the other polygonal bar is urged upward bysprings so that the rigid frame is swingable on the former polygonalbar, slots and holes are formed in the respective opposite ends of theconnecting bars, respectively, and the frame is assembled by fitting therespective opposite ends of the polygonal bars into the correspondingholes of the connecting bars and pressing the slotted outer ends of theconnecting bars with screws so as to fasten the polybonal bars to theconnecting bars.

According to a further aspect of the present invention, there isprovided an electromagnetic contactor of the same construction as thatof either one of the above-mentioned electromagnetic contactors, exceptthat the respective opposite ends of the connecting bars each has astepped part provided with a U-shaped groove and the end of thecorresponding polygonal bar is placed in the groove and fixed to thestepped part by screwing a member having the same U-shaped groove asthat of the stepped part for receiving the polygonal bar to the steppedpart of the connecting bar.

The above and other objects, features and advantages of the presentinvention will become more apparent from the following description ofthe preferred embodiments of the present invention taken in conjunctionwith the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a longitudinal sectional view of an electromagnetic contactor,in a first embodiment, according to the present invention;

FIG. 2 is a side elevation of the electromagnetic contactor of FIG. 1,in a state where the contacts are disengaged;

FIG. 3 is a side elevation of the electromagnetic contactor of FIG. 1,in a state where the contacts are engaged;

FIG. 4 is a sectional view taken along line IV--IV of FIG. 2;

FIG. 5 is a fragmentary exploded perspective view of a frame employed inthe electromagnetic contactor of FIG. 1;

FIG. 6 is a fragmentary sectional view of a connecting bar employed inthe first embodiment of FIG. 1, showing a bar fastening structure beforefastening;

FIG. 7 is a view similar to FIG. 6, showing the bar fastening structureafter fastening;

FIG. 8 is a longitudinal sectional view of an electromagnetic contactor,in a second embodiment, according to the present invention;

FIG. 9 is a side elevation of the electromagnetic contactor of FIG. 8,in a state where the contacts are disengaged;

FIG. 10 is a side elevation of the electromagnetic contactor of FIG. 8,in a state where the contacts are engaged;

FIG. 11 is a sectional view taken along line XI--XI of FIG. 9;

FIG. 12 is a fragmentary exploded perspective view of the frame employedin the second embodiment of FIG. 8;

FIG. 13 is a side elevation of an electromagnetic contactor, in a thirdembodiment, according to the present invention;

FIG. 14 is a fragmentary exploded perspective view of the frame employedin the third embodiment of FIG. 13;

FIG. 15 is an exploded perspective view of a connecting bar of the frameof a fourth embodiment of the present invention, showing a bar fasteningstructure;

FIG. 16 is a fragmentary sectional view of the clamping structure of aconnecting bar in a state before clamping a polygonal bar;

FIG. 17 is a fragmentary sectional view of the clamping structure ofFIG. 16 in a state after clamping the polygonal bar;

FIG. 18 is a perspective view of the clamping sections of connectingbars for assistance in explaining the manner of machining the ends ofthe connecting bars;

FIG. 19 is a perspective view of end portions of connecting barsemployed in the first, second and third embodiments of the presentinvention for assistance in explaining the manner of machining the endportions to form slots therein; and

FIG. 20 is a perspective view of the end portion of a connecting baremployed in the first, second and third embodiments of the presentinvention for assistance in explaining the manner of machining the endportion to form a hole therein.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The preferred embodiemnts of the present invention will be describedhereinafter in conjunction with the accompanying drawings, in which likereference characters designate like or corresponding parts throughout.

Referring to FIGS. 1 to 7 showing a first embodiment of the presentinvention, there are shown a base plate 1, an insulating stand 2fastened to the base plate 1 with screws 3, an E-shaped fixed core 4formed by laminating silicon steel plates, an operating coil 5 woundaround the central leg of the fixed core 4, a top plate 6 attached tothe upper end of the stand 2, crossbar guide walls 6a formed in thecentral portion of the top plate 6 so as to protrude upward, three pairsof terminal boards 7, namely, power supply terminal boards and loadterminal boards, provided on the top plate 6 on opposite sides,respectively, with respect to the crossbar guide walls 6a, and a pair offixed contacts 8, namely, a fixed power supply contact and a fixed loadcontact, attached through fixed contact bases 9 to each pair of theterminal boards, respectively.

A rectangular frame 10 consists of two parallel polygonal bars 10a andtwo parallel rectangular connecting bars 10b interconnecting therespective opposite ends of the polygonal bars, respectively. One of thepolygonal bars 10a is supported pivotally at the opposite ends thereofin bearings 2a supported on supporting parts 2b of the stand 2. A singlecrossbar 11 for three phases is formed of a synthetic resin and issupported pivotally at the lower portion thereof between the respectivecentral portions of the connecting bars 10b of the frame 11. There arealso shown in FIGS. 1 to 7, a movable core 12 received in a hollowformed in the lower portion of the crossbar 11, three pins 14 joiningthe movable core 12 to the crossbar 11, stop clips 15 attached to theopposite ends of the pins 14, a spring receiver 16 having a spring seat16a and attached to each connecting bar 10b on the free side of theframe 10, and a compression spring 17 extended between the spring seat16a and a spring seat attached to the stand 2 so as to urge the frame 10clockwise, as viewed in FIG. 1, namely, so as to move the movable core12 away from the fixed core 4. Three movable contact bars 18 each havinga pair of movable contacts 19 are mounted on top of the crossbar 13. Aspring seat 20 is fixed at the upper portion thereof to the uppersurface of each movable contact bar 18 with a rivet 21. A compressionspring 22 is extended between the spring seat 20 and a spring seat 20adisposed below the spring seat 20 so as to press the movable contact bar18 against the upper part of the crossbar 11.

Since the frame 10 is urged clockwise by the compression spring 17, theframe 10 is held at a predetermined upper position with the uppersurface of the crossbar pivotally mounted on the frame 10 in contactwith the top plate 6 while the operating coil 5 is not energized. Inthis state, the movable core 12 joined to the crossbar 11 is separatedfrom and is held opposite to the fixed core 4, while a pair of themovable contacts 19 provided on each movable contact bar 18 areseparated from and are held opposite to the corresponding fixed contacts8 provided on the fixed contact base 9. The gap between the fixedcontacts 8 and the movable contacts 19 is slightly smaller than the gapbetween the fixed core 4 and the movable core 12. Indicated at 23 is anarc box, at 24 is an auxiliary crossbar, at 25 is an auxiliary switchand at 26 is an auxiliary switch holding plate.

The manner of assembling the frame 10 and the mode of mounting thecrossbar 11 on the frame 10 will be described in connection with FIGS. 4to 7.

Slots 30 are formed in the opposite ends of each connecting bar 10b tobifurcate each end into a lower section 10b₁ and an upper section 10b₂.A square hole 31 is formed at the middle position of the slot 30. Thelength of the side of the square hole 31 is slightly greater than thewidth across the flats of the polygonal bar 10a and smaller than thewidth across the corners of the same. A bolt hole 30b is formedperpendicularly to the slot 30 in the outer portion of the lower section10b₁ and a threaded hole 30a is formed in alignment with the bolt hole30b in the upper section 10b₂ of the connecting bar 10b. One end of thepolygonal bar 10a, namely, a hexagonal bar in this embodiment, isinserted into the square hole 31 of the connecting bar 10b. Then, ascrew 32 is screwed through the bolt hole 30b into the threaded hole 30aformed in the upper section 10b₂ to clamp the end of the polygonal bar10a between the upper and lower sections 10b₂ and 10b₁ by forciblybending the upper and lower sections so that the inner surfaces of thesquare hole 31 are pressed against the polygonal bar 10a. Morespecifically, since the outer portions of the upper and lower sections10b₂ and 10b₁ are bent more than the inner portions of the same arebent, the square hole 31 is deformed into a trapezoidal shape, and hencethe inner surfaces of the square hole 31 come into contact with thepolygonal bar 10b along six lines A, B, C, D, E and F as illustrated inFIG. 7. That is, when the upper and lower sections 10b₂ and 10b₁ arebent, the inner surface of the square hole 31 are brought into contactwith the two corners of the polygonal bar 10a along contact lines A andB, while edges formed between the inner surfaces of the square hole 31and the surfaces of the slot 30 come into contact with the polygonal bar10a along four contact lines C, D, E and F as illustrated in FIG. 7.Thus the end of the polygonal bar 10a is held firmly by the connectingbar 10b so as to extend at right angles to the connecting bar 10b bybeing clamped firmly between the upper and lower sections 10b₂ and 10b₁formed in each end of the connecting bar 10b.

Pivots 35 projects from the respective central portions of the oppositeside faces of the crossbar 11. The pivots 35 are incorporated into thecrossbar 11 through insertmolding in forming the crossbar 11. The pivots35 are fitted pivotally into bearing holes 34 formed in the respectivemiddle position of the connecting bars 10b before assembling the frame10 by fastening the respective opposite ends of the polygonal bars 10ato the respective opposite ends of the connecting bars 10b,respectively.

When an AC voltage is applied to the operating coil 5, the operatingcoil 5 generates magnetic flux, and thereby the movable core 12 isattracted by the magnetic attraction of the fixed core 4 to the fixedcore 4 against the resilient force of the springs 17. Simultaneously,the crossbar 11 moves together with the movable core 12 toward the fixedcore 4, and thereby a pair of the movable contacts 29 of each movablecontact bar 18 held on the crossbar 11 come into contact with thecorresponding fixed contacts 8. Since the gap between the movable core12 and the fixed core 4 is greater than the gap between the movablecontact 19 and the corresponding fixed contact 8, the movable core 12,hence the crossbar 11, moves further toward the fixed core 4 after themovable contact 19 has come into contact with the corresponding fixedcontact 8. Consequently, the compression spring 22 is compressed, andhence the movable contacts 19 are pressed through the movable contactbar 18 against the corresponding fixed contacts 8 at a predeterminedcontact pressure.

Thus, when the movable core 12 is attracted against the resilient forceof the compression springs 17 by the fixed core 4, the frame 10 mountedpivotally with the crossbar 11 and the movable core 12 is turnedcounterclockwise as the movable core 12 is attracted by the fixed core4. If the attraction of the fixed core 4 acts irregularly, the movablecore 12 tends to move in a tilted position. However, since the crossbar11 joined to the movable core 12 is supported pivotally on the frame 10and the tortional regidity of the frame 10 tends to correct the tilt ofthe movable core 12 through the crossbar 11, the movable core 12 movestoward the fixed core 4 in the correct position. Accordingly, all themovable contacts 19 of the movable contact bars 18 mounted on top of thecrossbar 11 come simultaneously into contact with the correspondingfixed contacts 8.

When the operating coil 5 is de-energized, the magnetic attraction ofthe fixed core 4 acting on the movable core 12 is nullified.Consequently, the frame 10 is turned clockwise by the resilience of thecompressed compression springs 17, and thereby the crossbar 11 combinedwith the movable core 12 and pivotally supported on the frame 10 ismoved away from the fixed core 4, and hence the movable contacts 19 areseparated from the corresponding fixed contacts 8 and are returned tothe original position.

As described hereinbefore, in this embodiment, the crossbar combinedwith the movable core is supported pivotally on the connecting bars ofthe rigid frame formed by interconnecting the respective opposite endsof the two parallel polygonal bars by the two parallel connecting bars.Therefore, even if the magnetic attraction of the fixed core 4 actsirregularly on the movable core 12 to tilt the movable core 12, the tiltof the movable core 12 is corrected by the torsional rigidity of theconnecting bars 10b, and hence all the movable contacts provided on thecrossbar are brought simultaneously into contact with the correspondingfixed contacts.

A second embodiment of the present invention will be describedhereinafter in connection with FIGS. 8 to 12.

Basically, the construction of the second embodiment is similar to thatof the first embodiment, except that the second embodiment includesthree individual crossbars and a supporting case for pivotallyincorporating the three crossbars and a movable core to a rigid frame,hence to avoid duplication only the construction and components specificto the second embodiment will be described hereinafter and thedescription of those similar to or the same as those of the firstembodiment will be omitted.

Referring to FIGS. 8 and 11, a supporting case 13 is mounted pivotallyon a frame 10 so as to extend between the connecting bars 10b of theframe 10. A movable core 12 is accommodated in the supporting case 13,while three insulating crossbars 11 are mounted side by side on thesupporting case 13 so as to receive the supporting case 13 in therespective bottom portions thereof. The movable core 12 and the threecrossbars 11 are joined to the supporting case 13 with three pins 14,respectively. Indicated at 15 are stop clips attached to the oppositeends of the pins 14 to hold the three crossbars 11 and the movable corein place on the supporting case 13.

As illustrated in FIG. 12, the supporting case 13 has a body section 35having the form of a box, a pair of opposite end walls 36 formed in eachend portion of the body section 35 by bending the extremities of theside walls inward. A U-shaped supporting section 37 is formed at eachlongitudinal end of the body section by bending the extremity of theupper wall of the body section 35. A reinforcement 38 are screwed to theend walls 36 with screws 39. In mounting the supporting case 13pivotally on the frame 10, the respective central portions of theconnecting bars 10b and spacers 41 are received in the supportingsection 37, and then a bolt 40 is inserted through each supportingsection 37, the connecting bar 10b, the spacer 41 and the reinforcement38 in running fit and a hexagonal nut 42 is screwed on the threadedportion 40a of the bolt 40.

In this embodiment, when the operating coil 5 is energized to attractthe movable core 12 against the resilient force of the compressionsprings 17 by the fixed core 4, the frame 10 pivotally mounted with thesupporting case 13 integrally carrying the crossbars 11 and the movablecoil 12 is turned counterclockwise as the movable core 12 is attractedby the fixed core 4. Since the movable core 12 and the three crossbars11 are joined to the supporting case 13 with the pins 14, threecrossbars 11 are moved simultaneously toward the fixed core 4. If theattraction of the fixed core 4 acts irregularly on the movable core 12,namely, if the attraction acts more strongly on one side than on theother side of the movable core 12, the movable core 12 tends to movediagonally. However, since the supporting case 13 mounted with themovable core 12 is supported pivotally on the frame 10 and the tilt ofthe movable core 12 is corrected through the supporting case 13 by thetorsional resilience of the frame 10, the movable core 12 moves normallytoward the fixed core 4. Accordingly, the movable contacts 19 of themovable contact bars 18 mounted on top of the crossbars 11,respectively, are brought simultaneously into contact with thecorresponding fixed contact 8.

When the operating coil 5 is de-energized, the magnetic attraction ofthe fixed core 4 acting on the movable core 12 is nullified.Consequently, the frame 10 is turned clockwise by the resilience of thecompressed compression springs 17, and thereby the crossbars 11 and themovable core 12 joined to the supporting case 13 pivotally mounted onthe frame 10 are moved away from the fixed core 4, and hence the movablecontacts 19 are separated from the corresponding fixed contacts 8 andare returned to the original position.

As described hereinbefore, in the second embodiment, the movable core 12is accommodated in the supporting case 13, the three crossbars 11 aremounted on the supporting case so as to receive the supporting case 13in the respective recesses formed in the respective lower portions ofthe crossbars 11, respectively, and the movable core 12 and thecrossbars 11 are joined to the supporting case 13 by inserting the pins14 through the crossbars 11, the supporting case 13 and the movable core12 and attaching the stop clips to the respective opposite ends of thepins 14. Accordingly, the crossbars 11, the movable core 12 and thesupporting case 13 can be simply assembled. Furthermore, since thesecond embodiment is provided with three individual crossbars 11 eachfor one phase, the mold for molding the crossbars 11 is inexpensive, andthereby the crossbars can be manufactured at a low manufacturing cost.

A third embodiment of the present invention will be describedhereinafter in connection with FIGS. 13 and 14.

Basically, the construction and the performance of the third embodimentare similar to those of the second embodiment, except that the thirdembodiment has a hole formed in one of the connecting bars of the framefor receiving the tip of a screwdriver or the like to turn the frame sothat the movable contacts are brought into contact with thecorresponding fixed contacts for testing, hence to avoid duplicationonly the construction and components specific to the third embodimentwill be described hereinafter and the description of those similar to orthe same as those of the second embodiment will be omitted.

In this embodiment, the tip of a screwdriver is applied to a hole formedin one of the connecting bars 10b on the free side of the frame 10 andthe screwdriver is pushed to turn the frame 10 counterclockwise to bringthe movable contacts into contact with the corresponding fixed contactsfor testing. Since the distance between the center of turning of theframe and the hole for receiving the tip of a screwdriver is greaterthan the distance between the same center and the center of the movablecore, from the principle of leverage, the force required for pressingdown the screwdriver to turn the frame counterclockwise is smaller thanthe magnetic attraction of the fixed core to attract the movable core,and hence the frame can be easily turned manually.

Referring to FIGS. 13 and 14, in order to bring the movable contactsinto contact with the corresponding fixed contacts by manually movingthe movable core 12 toward the fixed core 4 to test the sequence circuitwith which the electromagnetic contactor is associated, the frame 10 isturned counterclockwise against the resilient force of the compressionsprings 17 by applying the tip of a screwdriver to the hole 34 formed inthe connecting bar 10b on the free side of the frame 10 and pressing thescrewdriver so as to move the movable core 12 toward the fixed core.Then, the frame 10 mounted with the crossbars 11, the supporting case 13and the movable core 12 is turned counterclockwise, and thereby themovable contacts 19 of the movable contact bars 19 mounted on thecrossbars 11, respectively, are brought into contact with thecorresponding fixed contacts 8, respectively. The force necessary toturn the frame 10 against the resilient force of the compression springs17 is smaller than the electromagnetic attraction of the fixed core 4,hence the frame 10 can be easily turned counterclockwise by pressing theconnecting bar 10b with the screwdriver.

As mentioned above, since the distance between the center of turning ofthe frame 10 and the hole 34 for receiving the tip of a screwdriver isgreater than the distance between the same center and the center of themovable core 12, from the principle of leverage, the force required forpressing down the screwdriver to turn the frame 10 counterclockwise issmaller than the magnetic attraction of the fixed core 4 to attract themovable core, and hence the frame 10 can be easily turned manually ascompared with turning a conventional assembly of links, crossbars and amovable core supported on the free ends of the links.

In the third embodiment, the hole 34 for receiving the tip of ascrewdriver is formed in one of the connecting bars 10b on the free sideof the frame 10 in the vicinity of the junction of the connecting bar10b and the polygonal bar 10a, however, naturally, the hole 34 may beformed in the polygonal bar 10a on the free side of the frame 10 in thevicinity of the junction of the connecting bar 10b and the polygonal bar10a or in an end plate 33 attached to the connecting bar 10b on the freeside of the frame 10 in the vicinity of the junction of the connectingbar 10b and the polygonal shaft 10a to receive the end of the polygonalshaft 10a.

Furthermore, although the third embodiment is provided with threecrossbars 11 arranged side by side, however, these three crossbars 11may be substituted by a large single crossbar.

A fourth embodiment of the present invention will be describedhereinafter in connection with FIGS. 15 to 18.

Basically, the construction and the performance of the fourth embodimentare similar to those of the first or second embodiment of the presentinvention, except that the construction of the frame 10 is differentfrom that of the frame of the first or second embodiment, hence to avoidduplication only the construction and components specific to the fourthembodiment will be described hereinafter and the description of thosesimilar to or the same as those of the first or second embodiment willbe omitted.

Prior to the description of the fourth embodiment, problems in machiningthe connecting bar 10b of the frame 10 employed in the first or secondembodiment will be explained.

In forming the slot 30 in each end of the connecting bar 10b, aplurality of flat steel bars 10b',i.e., materials of the connecting bars10b, arranged side by side as illustrated in FIG. 19 and the respectiveends of the flat steel bars 10b' are slotted with a saw blade A to formthe slots 30 in each end of each flat steel bar 10b'. Then, the squarehole 31 for receiving the end of the polygonal bar 10a, a hexagonal barin this embodiment, is formed in the middle of each slot 30 with a millB as illustrated in FIG. 20. When the hole 31 is machined with the millB, the corners of the hole 31 are inevitably rounded. If the radius ofthe rounded corners of the hole 31 is excessiveIy large, it isimpossible to insert the polygonal bar 10a into the hole 31. Therefore,only a mill having an extremely small diameter as compared with the sizeof the hole 31 is applicable to forming the hole 31. The connecting bars10b employed in the fourth embodiment can be machined efficiently with amill of any size at a low manufacturing cost.

The frame 10 of the fourth embodiment will be described hereinafter.Referring to FIGS. 15 to 18, indicated at 10a is a polygonal bar, i.e.,a hexagonal steel bar in this embodiment and at 10b is a connecting bar,i.e., a flat steel bar is this embodiment, for interconnecting the endsof the two parallel polygonal bars 10a. A clamping section 43 is formedin each end of the connecting bar 10b by milling substantially the halfportion of the end of the connecting bar 10b with a mill. Indicated at44 is an upper land formed at the inner end of the clamping section 43and at 43a is a lower land extending outward from the outer shoulder ofthe upper land 44. A groove 45 for receiving the polygonal bar 10a isformed practically at the middle of the lower land 43a so as to extendperpendicularly to the longitudinal axis of the connecting bar 10b. Boltholes 46 are formed in the upper land 44 and the outer end of the lowerland 43a of the clamping section 43. A clamping plate 47 to be combinedwith the clamping section 43 of the connecting bar 10b is formed bycutting a flat bar of a size practically the same as that of theclamping section 43. A groove 48 for receiving the polygonal bar 10a isformed at the middle of the clamping plate 47 so as to extend widthwiseof the clamping plate 47. Threaded holes 49 are formed in the oppositeends of the clamping plate 47 so as to be aligned with the bolt holes46, respectively, when the clamping plate 47 is attached to the clampingsection 43 of the connecting bar 10b. Screws 50 are inserted through thebolt holes 46 and screwed into the threaded holes 49, respectively, toclamp the polygonal bar 10a between the clamping plate 47 and theclamping section 43.

In machining the end of the connecting bar 10b to form the clampingsection 43 consisting of the upper land 44, the lower land 43a and thegroove 45, a plurality of the connecting bars 10b, for example, fourconnecting bars 10b, are arranged side by side as illustrated in FIG.18, then the ends of the connecting bars 10b are machined by a depthcorresponding to the level of the upper land 44 with a mill B, then thearea other than that corresponding to the upper lands 44 is machinedwith the mill B to form the lower land 43a, and then the grooves 45 arecut in the lower lands 43a with the mill B. When the diameter of themill B is not greater than the width of the grooves 45, the upper lands44, the lower lands 43a and the grooves 45 can be machined with the samemill.

Although not illustrated, the grooves 48 are formed simultaneously byarranging a plurality of the clamping bars 47 side by side and machiningthe clamping plates 47 similarly to machining the clamping sections 43with the mill B.

The polygonal bar 10a is fixed to the connecting bar 10b in thefollowing manner. The end of the polygonal bar 10a is fitted into thegroove 45 formed in the clamping section 43 of the connecting bar 10b,and then the clamping plate 47 is placed on the clamping section 43 withthe inner end thereof seated on the upper land 44 of the clampingsection and the groove 48 thereof receiving the polygonal bar 10atherein. The bolt 50 is inserted through the bolt hole 46 formed throughthe upper land 44 and screwed into the threaded hole 49 of the clampingplate 47 to fasten the clamping plate 47 to the upper land 44 of theclamping section 43, and then the screw 50 is inserted through the bolthole 46 formed in the outer end of the lower land 43a and is screwedinto the corresponding threaded hole 49 of the clamping plate 47. As thelatter screw 50 is screwed into the threaded hole 49, the clampingsection 43 and the clamping plate are bent toward each other, so thatthe inner surfaces of the groove 45 of the clamping section 43 and thegroove 48 of the clamping plate 47 are pressed firmly against thesurface of the polygonal bar 10a, and thereby the end of the polygonalbar 10a is clamped firmly between the clamping section 43 and theclamping plate 47. Since the bend of the clamping section 43 and theclamping plate 47 increases toward the outer ends of the clampingsection 43 and the clamping plate 47, the square hole formed by thegrooves 45 and 48 is deformed into a trapezoidal hole. Consequently, asshown in FIG. 17, the clamping section 43 of the connecting bar 10b andthe clamping plate 47 are brought into contact with the polygonal bar10a, namely, the hexagonal bar, along six lines A, B, C, D, E and F.Thus the respective ends of the polygonal bar 10a and the connecting bar10b are joined firmly together at right angles and it is impossible forthe polygonal bar 10a to move in the groove 45 of the clamping section43 and the groove 48 of the clamping plate 47, even if a vertical or alateral force is applied to the polygonal bar 10a.

Although the invention has been described with reference to thepreferred embodiment thereof with a certain degree of particularity, itis to be understood to those skilled in the art that various changes andmodifications may be made in the invention without departing from thespirit and scope thereof.

What is claimed is:
 1. An electromagnetic contactor comprising: a base;a stand fixed to the base plate; an electromagnet consisting of a fixedcore and an operating coil mounted on the fixed core, and disposedwithin the stand; a plurality of fixed contacts provided in the upperportion of the stand; a crossbar disposed above the fixed core; aplurality of contact bars each associated with the crossbar and providedwith a pair of movable contacts so that the movable contacts are locatedopposite the corresponding fixed contacts, respectively; a movable corejoined to the lower portion of the crossbar so as to be located oppositefixed core; and a rigid frame consisting of two parallel polygonal barsand two parallel connecting bars interconnecting the respective oppositeends of the polygonal bars, and pivotally supporting the assembly of thecrossbar and the movable core at the opposite ends of the movable core,wherein one of the polygonal bars is supported at the opposite endsthereof in bearings provided on one side of the stand, while the otherpolygonal bar is urged upward by springs so that the rigid frame isswingable on the former polygonal bar, a slot is formed in each end ofeach connecting bar so as to extend longitudinally of the connectingbar, the middle portion of the slot is expanded to form a hole forreceiving one end of the polygonal bar perpendicularly to the connectingbar, and the frame is assembled by fitting the respective opposite endsof the polygonal bars into the corresponding holes of the connectingbars and pressing the slotted outer ends of the connecting bars withscrews so as to fasten the polygonal bars to the connecting bars.
 2. Anelectromagnetic contactor according to claim 1, wherein said polygonalbars are hexagonal bars.
 3. An electromagnetic contactor according toclaim 2, wherein said holes formed in the middle portion of the slots ofsaid connecting bars are substantially square holes, respectively.
 4. Anelectromagnetic contactor according to claim 1, wherein each end portionof each said connecting bar is cut to form a clamping section having anupper land, a lower land and a groove formed in the middle portion ofthe lower land so as to extend widthwise of the connecting bar, one endof said polygonal bar is placed in the groove of the clamping section, aclamping plate having a groove formed so as to correspond to the grooveof the clamping section when the same is atttached to the connecting baris placed on the clamping section with the inner end thereof seated onthe upper land and the groove thereof receiving the end of the polygonalbar therein, and the opposite ends thereof are screwed to the clampingsection so that the end of the polygonal bar is clamped firmly in thegrooves between the clamping section and the clamping plate.
 5. Anelectromagnetic contactor comprising: a base plate; a stand fixed to thebase plate; an electromagnet consisting of a fixed core and an operatingcoil mounted on the fixed core, and disposed within the stand; aplurality of fixed contacts provided in the upper portion of the stand;a supporting case; plurality of crossbars mounted on the supporting caseand joined to the same with pins, respectively; a plurality of contactbars associated with the crossbars, respectively, and each provided witha pair of movable contacts so that the movable contacts are locatedopposite the corresponding fixed contacts, respectively; a movable coredisposed within the supporting case and joined to the same with the pinsjoining the crossbars to the supporting case, so as to be locatedopposite the fixed core; and a rigid frame consisting of two parallelpolygonal bars and two parallel connecting bars interconnecting therespective opposite ends of the polygonal bars, and pivotally supportingthe supporting case at the opposite ends of the same, wherein one of thepolygonal bars is supported rotatably at the opposite ends thereof inbearings provided on one side of the stand, while the other polygonalbar is urged upward by springs so that the rigid frame is swingable onthe former polygonal bar, a slot is formed in each end of eachconnecting bar so as to extend longitudinally of the connecting bar, themiddle portion of the slot is expanded to form a hole for receiving oneend of the polygonal bar perpendicularly to the connecting bar, and theframe is assembled by fitting the respective opposite ends of thepolygonal bars into the corresponding holes of the connecting bars andpressing the slotted outer ends of the connecting bars with screws so asto fasten the polygonal bars to the connecting bars.
 6. Anelectromagnetic contactor according to claim 5, wherein said polygonalbars are hexagonal bars.
 7. An electromagnetic contactor according toclaim 5, wherein said holes formed in the middle portion of the slots ofsaid connecting bars are substantially square holes, respectively.
 8. Anelectromagnetic contactor according to claim 5, wherein each end portionof each said connecting bar is cut to form a clamping section having anupper land, a lower land and a groove formed in the middle portion ofthe lower land so as to extend widthwise of the connecting bar, one endof said polygonal bar is placed in the groove of the clamping section, aclamping plate having a groove formed so as to correspond to the grooveof the clamping section when the same is attached to the connecting baris placed on the clamping section with the inner end thereof seated onthe upper land and the groove thereof receiving the end of the polygonalbar therein, and the opposite ends thereof are screwed to the clampingsection so that the end of the polygonal bar is clamped firmly in thegrooves between the clamping section and the clamping plate.
 9. Amagnetic contactor according to any one of claims 1 to 8, wherein a holefor receiving the tip of a screwdriver or the like is formed in one ofsaid connecting bar at a position in the vicinity of the junction of theconnecting bar and the polygonal bar on the free side of said frame, inorder to facilitate the manual turning of said frame to bring themovable contacts manually into contact with the corresponding fixedcontacts.